444 



The Control of Onion Smtjt. [Aug,, 



whether the disease at Crookham-on-Tweed was introduced by 

 the use of contaminated Scottish seed. At one centre (Wylam) 

 the grower is of the opinion that the Smut foUov/ed the purchase 

 of an unusually large quantity of seed consequent upon the 

 decision to increase the acreage under onions ; but he is unable to 

 recollect the locality from which the seed was purchased. It 

 appears to be definitely estabHshed that Onion Smut can be 

 carried by means of contaminated seed.* 



So far as the writer is aware the total acreage infected in 

 Northumberland is as follows : — Crookham-on-Tweed, J acre ; 

 Wylam-on-Tyne, 7 acres, and one B-acre field on the eastern 

 boundary of the village ; Horsley, one 3-acre field and three 

 separate plots of J acre each. A further small plot at Whitley 

 Bay is possibly infected since it is known that seedling onions 

 grown in infected soil have been planted there. 



All the plots except the fi^rst and last are cultivated by the 

 same grower, and in all probability the disease has been carried 

 (from one field to another on the boots or implements of the 

 workmen. Examination of neighbouring gardens failed to reveal 

 any signs of Smut. 



The system of cultivation on all the infected plots follows 

 the usual lines except that most of the crop is left unthinned. 

 The only manure used is either farmyard or stable manure, and 

 the seed is drilled in rows about 12 in. apart. At Wylam, the 

 main sowing is done in August, the crop being sold the following 

 spring as " scallions " for the table. The practice at Crook- 

 ham, however, is to sow in spring, usually for sale as transplants. 



The actual date of sowing has little effect upon the intensity 

 of attack, this being very largely determined by the kind of 

 growing weather experienced. Autumn-sown crops usually suffer 

 much more severely than do spring-sown, and a diy growing 

 season undoubtedly results in a greater loss from smut than is 

 to be expected if the season is warm and moderately damp. 



Experiments on Controlling the Disease. — The first attempt 

 to control the disease was made by W. B. Mercer, in 1915, at 

 Wvlam, on a plot of land which had carried gooseberry bushes 

 for 16 years and had never been under onions within the 

 memory of the grower.! 



«G. H. Chapman, Mass., Sta. Rpt., 1909, pt. 1, pp. 164-167. 



f The question as to how this plot became infected can now be merely a 

 subject for speculation. Since the plot is centrally placed in a if^arden which 

 is badly infected, there is little doubt that both wind-borne spores and spores 

 carried on the boots and implements of the g-ardeners have contributed 

 to the dissemination of the disease. The possibility, however, of surface 

 drainag-e water playing its part in distributing the spores should not be 

 overlooked. 



